Astronomers have discovered a key signpost of rapid star
formation in a galaxy 11 billion
light-years from Earth,
seen as it was when the Universe was only 20 percent
of its current age. Using the National Science Foundation's
Very Large Array (VLA) radio telescope, the scientists
found a huge quantity of dense interstellar gas -- the
environment required for active star formation -- at the
greatest distance yet detected.

A furious spawning of the equivalent of 1,000 Suns per
year in a distant galaxy dubbed the Cloverleaf may be
typical of galaxies in the early Universe, the scientists
say.

VLA image (green) of radio emission
from HCN gas, superimposed on Hubble
Space Telescope image of the Cloverleaf
galaxy. The four images of the Cloverleaf
are the result of
gravitational lensing.

CREDIT: NRAO/AUI/NSF, STScI(Click on Image for Larger Version)

"This is a rate of star formation more than 300 times
greater than that in our own
Milky Way and similar
spiral galaxies, and our discovery may provide important
information about the formation and evolution of galaxies
throughout the Universe," said Philip Solomon, of
Stony Brook University in New York.

Solomon and Vanden Bout worked with Chris Carilli of NRAO
and Michel Guelin of the
Institute for Millimeter Astronomy
in France. They reported their results in the December 11
issue of the scientific journal Nature.

In galaxies like the Milky Way, dense gas traced by HCN but
composed mainly of hydrogen molecules is always associated
with regions of active star formation. What is
different about the Cloverleaf is the huge quantity of
dense gas along with very powerful infrared radiation
from the star formation. Ten billion times the mass of the
Sun is contained in dense, star-forming gas clouds.

"At the rate this galaxy is seen to be forming stars, that
dense gas will be used up in only about 10 million years,"
Solomon said.

In addition to giving astronomers a fascinating glimpse of
a huge burst of star formation in the early Universe, the
new information about the Cloverleaf helps answer a
longstanding question about bright galaxies of that era.
Many distant galaxies have
supermassive black holes at
their cores, and those
black holes power "central engines"
that produce bright emission. Astronomers have wondered
specifically about those distant galaxies that emit large
amounts of infrared light, galaxies like the Cloverleaf
which has a black hole and central engine.

"Is this bright infrared light caused by the black-hole-powered
core of the galaxy or by a huge burst of star formation?
That has been the question. Now we know that, in at least
one case, much of the infrared light is produced by intense
star formation," Carilli said.

The rapid star formation, called a
starburst,
and the black hole are both generating the bright infrared
light in the Cloverleaf. The starburst is a major event in
the formation and evolution of this galaxy.

"This detection of HCN gives us a unique new window through which
we can study star formation in the early Universe," Carilli
said.